This is a disorder where the nail separates from the nail bed (usually only part of and not the whole nail). It results from a build-up of debris found in the moist warm space between the digits, which attracts bacteria and fungal organisms, and in severe cases turns the nail plate a dark green or black colour.

The infected nail plate grows faster than those that are uninfected. In feet, onycholysis occurs through wearing a tight-pinching shoe, poor general circulation and lack of attention to foot care.